And yes, the stream of controlled Windows 8 leaks continues. This time around, Thurrot and Rivera have published a number of screenshots from Windows 8's brand-new tablet user interface, and surprise surprise, its built on Metro, the same design language that underpins Windows Phone 7. Windows 8 will also include its own PDF reader, Modern Reader, which also happens to be the first application packaged in Microsoft's new AppX format. Update: Long Zheng has some technical details on AppX, including this little tidbit: "The extensive list of properties signifies the comprehensive scope of this system to be the ideal deployment strategy for 'applications', in all essence of the word. In fact, the AppX format is universal enough so it appears to work for everything from native Win32 applications to framework-based applications and even *gasp* web applications. Games are also supported."

Adobe makes money on the authoring tools (and maybe licensing the format; not sure about this). Having Windows being able to handle PDFs out of the box would only boost them.

At face value, that's all fair enough.

The greater concern with Microsoft, though, would be proprietary extensions. If their PDF reader allows features to be added to PDFs that the real spec doesn't support, and authors target their PDFs at the Windows majority (or worse, MS Office-produced PDFs don't display properly without them), then the format has been EEEd, and the only solution is in court. But I don't think pre-emptive legal action will be possible; Adobe will have to wait and see if Microsoft plays fair.